Answer architecture round 5: the shipped packages are enus, svse, geose, geous and misc, each holding its files at its root under its manifest's namespace, and the errors use the wording a bench of the Audience chose

CHANGELOG.md

@@ -126,13 +126,14 @@ replacement, and each removed path, column or flag.
   `sv_SE.sex[f].first-name[Kim]`, and a category with no columns names the record
   that gives it one.
 - The shipped data comes in Go packages, one per module, each exporting `FS`:
-  `github.com/larvit/fejkdata/data/en_US`, `…/sv_SE`, `…/misc`, `…/geo/SE` and
-  `…/geo/US`. `data.Modules()`, from `github.com/larvit/fejkdata/data`, lists every one,
+  `github.com/larvit/fejkdata/data/enus`, `…/svse`, `…/misc`, `…/geose` and
+  `…/geous`. `data.Modules()`, from `github.com/larvit/fejkdata/data`, lists every one,
   and the CLI carries them all. `New` loads the modules `WithDataFS(modules...)` names and
   the folders `WithDataPath` names, and fails, naming `WithDataFS`, where no such option
-  is given. A manifest's `reads` lists the modules its source reads by default, and a
-  reference to a path nothing provides fails to load, naming every module the loaded
-  manifests read, or saying there are none.
+  is given. A manifest's `namespace` mounts its source under a dot path, and its `reads` lists the
+  modules its source reads by default; a reference to a path nothing provides fails to
+  load, asking whether a module is missing and naming every module the loaded manifests
+  read, or saying there are none.
 - A data source whose root holds a `.fejkdata.json` manifest with an `index` loads each
   category on the first call reaching it, as each shipped module does. Data failing to load,
   in `New` or on that first call, gives an error matching `ErrLoad`, and the CLI exits 1.